High-density high-energy anisotropically permanent magnet

ABSTRACT

A permanent magnet consisting of a compact mass of magnetically anisotropic powder having a theoretical density of which is at least 85 percent of the theoretical density and the magnetization in the direction of magnetization is at least 90 percent of the saturation magnetization.

United StatesPatent 1191 Westendorp et a1.

[11] 3,821,034 1451 'June 28, 1974 HIGH-DENSITY HIGH-ENERGY ANISOTROPICALLY PERMANENT MAGNET Inventors: Frans Frederik Westendorp; Willem Luiten; Giisbertus Maria Arnolds Josephus De Kort, all of Emmasingel, Eindhoven,

Netherlands Assignee: U.S. Philips Corporation, New

York, N.Y.

Filed: July 16, 1971 Appl. No.: 163,472

Related U.S. Application Data Division of Ser. No. 871,893, Oct. 28, 1969. Pat. No. 3,615,915.

Foreign Application Priority Data Oct. 31, 1968 Netherlands 6815510 U.S. Cl 148/3L57, 148/103, 148/105,

' 264/24 Int. Cl. H01f 1/04 Field of Search 148/103, 105, 101, 31.57; 264/24, 65, 60, DIG. 50, 62

OTHER PUBLICATIONS Buschow et a1; Magnetic Material With a BH of 18.5 X 10 Gauss-Oersteds; in Philips Tech, R ey., No. 11, 1968, pp. 336-337.

Primary Examiner-Walter R. Satterfield Attorney, Agent, or Firm-Frank R. Trifari; Carl P. Steinhauser 5 7 ABSTRACT A permanent magnet consisting of a compact mass of magnetically anisotropic powder-having a theoretical density of which is at least 85 percent of the theoretical density and the magnetization in the direction of magnetization is at least 90 percent of the saturation magnetization.

2 Claims, 1 Drawing Figure PATENTED JUE 2 8 W W v w M H T JZ E1 21% W I W ht. y y 1 Q 7% HIGH-DENSITY HIGH-ENERGY ANISOTROPICALLY PERMANENT MAGNET This application is a division of application Serial No. 871,893, filed Oct. 28, 1969, now US. Pat. No. 3,615,915.

The invention relates to a method of densifying magnetically anisotropic powders, for example, powders of ferromagnetic metals, metal alloys or ceramic materials into solid magnetic bodies, in which method a powdery mass is subjected to an external magnetic field which orientates the powder particles, said mass being densified by compression.

It is common practice to subject the previously orientated powder, as the case may be, subsequent to preliminary densification at low pressure, to a high pressure in a mold by one die or one lower and one upper die. It has to beendeavoured to maintain the orientation of the particles in order to obtain satisfactory permanent magnetic properties. 1

Such a densifying method has various disadvantages. In the first place the orientated powder is not densified homogeneously so that the relative orientation of the powder particles (alignment)is changed and hence the magnetisation in the direction of magnetisation is adversely affected. During compression the powder mass is locally deformed to a great extent mainly due to friction along the wall. This has an unfavourable influence on the orientation of the particles and hence on the magnetisation in the direction of magnetisation. It has,

moreover, been found that in the known compression methods the attainable density and hence the attainable magnetisation of the compressed powder are limited. There appears a strange phenomenon in that however high the pressure is raised the density of the compressed powder does not exceed a given value. For example, in compressing barium hexaferrite it has not been possible to attain a density exceeding 60 percent of the theoretical density.

This phenomenon has not yet been satisfactorily accounted for. A fact is, however, that the attempts to increase magnetisation by increasingthe density by compression have so far failed due thereto.

The present invention has for its object to obviate said disadvantage and to overcome the barrier to the increase in magnetisation by an increased density obtained by compression.

For this purpose the method according to the invention is characterized in that the powdery mass is compressed by an isostatic pressure of at least 10 kbar, and that it is slightly deformed anisotropically plastically, the said isostatic pressure being maintained.

It has been found that by isostatic compression a homogeneous densification of the powdery mass is ob-' tained, while the orientation of the particles is maintained. During the subsequent slight anisotropic, plastic deformation, while the isostatic pressure is maintained, asurprisingly considerable increase in density is obtained, whereas the orientation of the particles is hardly affected by this deformation. These two measures provide a magnet having a considerably higher energy product (BI-1M than could hitherto be obtained.

The invention furthermore relates to a permanent magnet manufactured of magnetically anisotropic powderby the method described above. The permanent magnet is characterized in that the density is at least 85 percent of the theoretical density and the magnetisation in the direction of magnetisation is at least 90 percent of the saturation magnetisation.

An advantageous permanent magnet embodying the invention is characterized in that the essential constituent of the powder is a compound of hexagonal structure, the existence range of which is integral with the existence range of the compound in the system M-R that is M R, wherein M is Co or a combination of Co with one or more of the elements Fe, Ni and Cu and R designates one or more of the elements of the rare earth metals and/or Th and/or Y.

Such powders are known from Dutch Pat. Application No. 6,608,335 and are particularly suitable for providing in conjunction with the method according to the invention permanent magnets having very high (Bl-U values.

In a further advantageous permanent magnet embodying the invention M is Co and R is Sm, while the energy product (BH),, has a value of at least 14Xl0 Gauss Oersted. The energy product (Bl-1),, of this magnet is considerably higher than that of the SmCo magnets hitherto known. From the review Joumal of Applied Physics, Vol. 39, No. 3, 1968, pages 1,719 1,720 it is known, for example, that an SmCo magnet on which a (BHL value of 8.1 X 10 Gauss Oersted had been measured, whereas the present magnet attains values of 15 X 10 Gauss Oersted and higher.

By way of example the invention will be. described more fully with reference to the drawing.

Magnetically anisotropic powder is put into a rubber bag and disposed in a magnetic field so that the powder particles are orientated. While the magnetic field is maintained, the powder is compressed until a coherent block of particles is obtained.

Then the rubber bag with its contents is evacuated and sealed in an air-tight manner. The block is then isostatically predensified (for example at a pressure of 8 kbar) and after the compression the rubber bag is removed.

The isostatic pre-densification may be carried out by hydrostatic means.

The block is then introduced in a container of ductile material. The container is sealed by a covering plate, which may be soldered to the container. Then the container is compressed at a high isostatic pressure of, for example, 20 kbar and while this high pressure is maintained it is slightly deformed anisotropically and plastically. This compression may be carried out hydrostatically in a press having, in addition, the means for performing said plastic deformation. Such a press may be constructed as is shown schematically in the Figure.

Reference numeral 1 designates a compression vessel having a shoulder 2 on the inner side. The vessel has a space 3 filled with liquid. In order to prevent the liquid from changing into the solid state at the high pressures of the order of 7 kbar, petrol is used as a pressure transmitting medium. Other appropriate liquids may be chosen for this purpose.

The space 3 is bounded on the lower side by a plunger 4, which is adapted to reciprocate in the compression vessel by means of a hydraulic worm 5, connected therewith, and on the upper side by a plunger 6, which is connected with a hydraulic worm 7 and is also adapted to reciprocate in the compression vessel. The hydraulic worms 5 and 7 can be driven independently of each other.

In the space 3 between the shoulder 2 and the plunger 6 two loose dies 8 and 9 are provided, between which is arranged the aforesaid, hermetically closed container 10 containing the block of magnetically orientated material. The container may be introduced into the vessel by removing the plunger 6. The assembly of the compression vessel, the dies and the hydraulic worms is arranged in a frame 11.

The press operates as follows:

By actuating the worms and 7 each of the plungers 4 and 6 exert equal high pressures on the liquid in the space 3. The hydrostatic pressure is exerted on the container 10, which is thus compressed, the orientated powder contained therein being homogeneously densified. Then the pressure exerted by the plunger 6 is slightly raised, whereas the pressure exerted by the plunger 4 is kept constant. The assembly of plungers 4 and 6 and the liquid column thus move slowly downwards. At a given instant the plunger 6 touches the die 8 and the container is slightly deformed. By means of the die 8 an anisotropic plastic deformation is obtained. It has, of course, to be ensured that liquid can always flow along the dies 8 and 9, for example, by providing holes therein.

After the hydrostatic compression of the container 10 and the slight anisotropic, plastic deformation, the pressure of the plungers is obviated and the container can be removed from the compression vessel and be opened.

Although only one form of the method according to the invention is described herein, presses of different constructions may of course also be employed.

Example Powder of SmCo having an average particle size of less than 10 ,um was orientated in a magnetic field of 30,000 Oersted and then hydrostatically predensified to percent of the theoretic density. The resultant material was hermetically enclosed in a lead container then hydrostatically compressed and slightly deformed anisotropically and plastically in the manner described above. The hydrostatic pressure was 20 kbar. The result was an SmCo magnet having a density amounting to 93 percent of the theoretic density. The energy product (BHL was 18.5 X 10 Gauss Oersted.

What is claimed is:

l. A high-density high-energy anisotropically permanent magnet consisting of a predensified and isostatically compacted coherent mass of magnetically anisotropic magnetic powder consisting essentially of a compound having a hexagonal crystal structure isomorphous with that of the compound M R wherein M is Co or a combination of Co and an element of the group consisting of Fe, Ni and Cu and R is an element selected from the group consisting of Y, Th, and the rare earth metals having a density which is at least percent of the theoretical density and a magnetization in the direction of magnetization of at least percent of the saturation magnetization.

2. A permanent magnet as claimed in claim 1 in which M is Co and R is Sm and said magnet has an energy product (811), of at least 14 X 10 Gauss-Oersted 

2. A permanent magnet as claimed in claim 1 in which M is Co and R is Sm and said magnet has an energy product (BH)Max of at least 14 X 106 Gauss-oersted 